The present invention relates to pneumatic instruments which receive a pressurized gas supply input and an electric control input to provide a regulated pneumatic output as a function of the electric control input. Such instruments are herein referred to as I/P transducers, because the electric control input is ordinarily an electric current "I" and the output is ordinarily a pneumatic pressure "P". In particular, the invention relates to particle trapping devices for I/P transducers.
The user of an I/P transducer provides the pneumatic gas supply input to the unit, which gas supply often includes particles entrained therein. Present I/P transducers employ filters of various types to remove such particles from the pneumatic line before they can distort the transducer output or otherwise damage the unit. Particles can distort the I/P transducer output by abrading precision components or by plugging small orifices of the I/P transducer. Filters used to remove such particles include wire mesh screens and combination filter-regulator devices, the latter of which are often attached directly to the input port of the I/P transducer housing. Such filters do an effective job of removing most of the harmful particles, thereby improving reliability of the I/P transducer.
However, in some installations the user's pneumatic air supply includes particles which stick to and accumulate on sensitive parts of the I/P transducer, and which the prior art filters do not effectively filter out. These particles are herein referred to as "sticky" particles. They are believed to comprise a combination of oil droplets, rust, and water vapor.